import 'package:flutter/material.dart';

class WrapAndFlowWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Column(
      children: <Widget>[
        Text(
          '流式布局Wrap',
          style: TextStyle(
            fontSize: 30.0,
          ),
        ),
        Text('''spacing：主轴方向子widget的间距
runSpacing：纵轴方向的间距
runAlignment：纵轴方向的对齐方式''',style: Theme.of(context).textTheme.title,),
        Wrap(
          //流式布局
          spacing: 8.0, // 主轴(水平)方向间距
          runSpacing: 4.0, // 纵轴（垂直）方向间距
          alignment: WrapAlignment.center, //沿主轴方向居中
          children: <Widget>[
            Chip(
                avatar: CircleAvatar(
                  backgroundColor: Colors.blue,
                  child: Text('A'),
                ),
                label: Text('Hamilton')),
            Chip(
              avatar:
                  CircleAvatar(backgroundColor: Colors.blue, child: Text('M')),
              label: Text('Lafayette'),
            ),
            Chip(
              avatar:
                  CircleAvatar(backgroundColor: Colors.blue, child: Text('H')),
              label: Text('Mulligan'),
            ),
            Chip(
              avatar:
                  CircleAvatar(backgroundColor: Colors.blue, child: Text('J')),
              label: Text('Laurens'),
            ),
          ],
        ),
        Text(
          '流式布局Flow',
          style: TextStyle(fontSize: 30.0),
        ),
        Flow(
          delegate: TestFlowDelegate(margin: EdgeInsets.all(10.0)),
          children: <Widget>[
            Container(
              width: 80.0,
              height: 80.0,
              color: Colors.red,
            ),
            Container(
              width: 80.0,
              height: 80.0,
              color: Colors.green,
            ),
            Container(
              width: 80.0,
              height: 80.0,
              color: Colors.blue,
            ),
            Container(
              width: 80.0,
              height: 80.0,
              color: Colors.yellow,
            ),
            Container(
              width: 80.0,
              height: 80.0,
              color: Colors.brown,
            ),
            Container(
              width: 80.0,
              height: 80.0,
              color: Colors.purple,
            ),
          ],
        ),
      ],
    );
  }
}

class TestFlowDelegate extends FlowDelegate {
  EdgeInsets margin = EdgeInsets.zero;

  TestFlowDelegate({this.margin});

  @override
  void paintChildren(FlowPaintingContext context) {
    var x = margin.left;
    var y = margin.right;
    //计算每个子Widget的位置
    for (int i = 0; i < context.childCount; i++) {
      var w = context.getChildSize(i).width + x + margin.right;
      if (w < context.size.width) {
        context.paintChild(i,
            transform: new Matrix4.translationValues(x, y, 0.0));
        x = w + margin.left;
      } else {
        x = margin.left;
        y += context.getChildSize(i).height + margin.top + margin.bottom;
        //绘制子widget(有优化)
        context.paintChild(i,
            transform: new Matrix4.translationValues(x, y, 0.0));
        x += context.getChildSize(i).width + margin.left + margin.right;
      }
    }
  }

  getSize(BoxConstraints constraints) {
    //指定Flow的大小
    return Size(double.infinity, 200.0);
  }

  @override
  bool shouldRepaint(FlowDelegate oldDelegate) {
    return oldDelegate != this;
  }
}
